1. Field of the Invention
This invention relates generally to the control of an inductively controlled multi-phase motor. More specifically, it relates to the control of a stepper motor whose rotational motion is translated into linear motion.
2. Description of the Prior Art
In the prior art, the braking of an inductively controlled multiphase motor is achieved by measuring time. Typically, a circuit is triggered and the motor activated. At some later time, the braking is applied. This type of braking results in mechanical vibration that is undesirable, and requires sophisticated implementation to work properly. The problems associated with smooth start-up and stopping are not easily overcome when the criterion for such motion is based upon time alone.
In the disclosed system, when the motion is continuous, braking is achieved by applying current to lagging phases in such a way that the stopping of the rotation is accomplished in accordance with an RC time constant voltage detent. When the motor is operated in a stepping fashion, a lagging phase is applied after a desired rotational phase has been selected. The lagging phase is applied for a predetermined time period ending prior to the time required to move from detent to the position desired by the selected phase. Then, the selected phase is again activated so that the motor rotor again detents at the desired pole. In combination with this type of braking is a simplified circuit for causing more or less motor current to flow, as determined by the amplitude of charge on a capacitor when the lagging phase or phases is selected.